Exhaust systems are used in combustion engines to manage exhaust gas produced through combustion operation in engine cylinders. The exhaust systems may include exhaust manifolds, emission control devices, mufflers, etc. However, vehicle designs may impose packaging constraints on the exhaust system to achieve a desired vehicle profile or compactness. However, these packaging constraints may be at odds with various functional characteristics of the exhaust system such as emission control device operation, turbine operation, back pressure generation, etc. For example, shortening an exhaust manifold may lead to increased back pressure generation and/or create uneven flow distribution for downstream components such as a catalyst. Therefore, trade-offs may be made between vehicle compactness and the functional characteristics of the exhaust system.
U.S. Pat. No. 7,997,071 discloses an exhaust flow distribution device positioned in a muffler upstream of an integrated exhaust aftertreatment device, such as a catalyst or diesel particulate filter. The flow distribution device disrupts the exhaust gas flow travelling through the muffler.
The Inventors have recognized several drawbacks with the exhaust flow distribution device discloses in U.S. Pat. No. 7,997,071. For example, the flow distribution device may not uniformly distribute exhaust gas. For instance, wakes may be generated behind the deflectors in the flow distribution device, thereby decreasing velocity distribution of the exhaust gas directly behind the flow distribution device. Furthermore, this device is suited to exhaust flows that are centrally discharged into a symmetric catalyst inlet cone, and not a compact exhaust manifold.
The inventors herein have recognized the above issues and developed an exhaust system for an engine. The exhaust system includes an emission control device and an exhaust manifold having a plurality of runners merging at a confluence section positioned upstream of the emission control device. The exhaust system further includes a mixer plate positioned in the confluence section, the mixer plate including a central opening and a plurality of louvered vents positioned axially around the central opening, the louvered vents having angled openings facing a common rotational direction.
The mixer plate may enable the exhaust gas flow provided to the downstream emission control device to be more evenly distributed. As a result, emission control device operation may be improved. Specifically, in one example, the tangential exhaust gas flow generated via the exhaust runners works in conjunction with the angled louvered vents to decrease velocity variability in the exhaust gas. As a result, the gas flow from the individual runners of the compact exhaust manifold are less likely to use separate zones of the catalyst brick, thereby improving the conversion efficiency of the emission control device. This is especially true when the air-fuel ratio from each cylinder is not stichiometric. Further, it will be appreciated that the mixer plate may not significantly increase backpressure in the exhaust manifold, which may degrade high load performance (e.g., full load performance), due to the central opening in the mixer plate. As a result, a compact exhaust manifold may be used in the exhaust system, if desired, without significantly increasing backpressure or decreasing the exhaust gas conversion efficiency in the emission control device. Thus, traditional trade-offs between desired characteristics in the exhaust system discussed above may be circumvented.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Additionally, the above issues have been recognized by the inventors herein, and are not admitted to be known.